What is offline UPS?

Offline UPS protects against many problems in your network. Under normal conditions it conducts the input current to its outlet. When the power supply fails it switches over to a built in battery to compensate for any variations in the mains supply.

Offline UPS Definition

Offline UPS – also referred to as VFD (Voltage and Frequency Dependent) or Standby UPS – offer the most basic level of power protection.

When the mains supply fails or fluctuates outside of the UPS’s operating window, a relay connects the load to the inverter output (resulting in a 4-8ms transfer time). In normal operation, with mains supply present, both output voltage and frequency will track the input voltage and frequency respectively.

Working principle

Look at the offline UPS diagram below，you will understand why people also call it a “backup” or stand-by UPS.

Common power problems

The primary role of any UPS is to provide short-term power when the input power source fails. However, most UPS units are also capable in varying degrees of correcting common utility power problems:

Voltage spike or sustained overvoltage
Momentary or sustained reduction in input voltage
Voltage sag
Noise, defined as a high frequency transient or oscillation, usually injected into the line by nearby equipment
Instability of the mains frequency
Harmonic distortion, defined as a departure from the ideal sinusoidal waveform expected on the line

Advantages of Offline UPS

Compared with online UPS price，offline UPS’s are cheaper.
High efficiency, making it the most commonly used for providing power supply for personal computers and is also used for office supply.
Smaller size. The stand by UPS is available in small and compact sizes which is important when there is no big space available. Its compact size makes the stand by UPS’s first choice when it comes to supplying computers in-home use.

In a word, you can buy an offline ups to protect your equitment from power failure, sags and surges in a low price, but if you want a UPS which can offers total power protection, you should get an online ups rather than offline.